SGP/SIRS/E3 - Instrument leveling and tracker problem

Asymmetry between measured downwelling shortwave and derived downwelling shortwave 
hemispheric in the afternoon began late in fall and became more apparent as the sun moved higher 
in spring.  This can happen when the PSP is unlevel or when the NIP is not tracking well. 

The PSP level was corrected and the clock on tracker was reset.  Mentor suspects PSP was 
unlevel during this time range causing the discrepancy in measured vs. calculated 
downwelling shortwave hemispheric data.

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• Instantaneous Downwelling Hemispheric Shortwave, Pyranometer Thermopile Voltage(inst_global)
• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)
• Instantaneous uncorrected downwelling shortwave diffuse, shaded pyranometer
  thermopile voltage(inst_diffuse)

• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyranometer, Standard
  Deviation(down_short_diffuse_hemisp_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Downwelling shortwave diffuse hemispheric irradiance, pyranometer, maxima(down_short_diffuse_hemisp_max)
• Downwelling shortwave hemispheric irradiance, pyranometer, maxima(down_short_hemisp_max)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
  Deviation(down_short_hemisp_std)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyrgeometer, Minima(down_short_diffuse_hemisp_min)
• Down-welling unshaded pyranometer voltage(down_short_hemisp)
• Downwelling Shortwave Hemispheric Irradiance, Pyranometer, Minima(down_short_hemisp_min)